Re: Kernel oops in resched_task() with 2.6.31.5

[Kenji Kaneshige]

Kenji Kaneshige wrote:
> Peter Zijlstra wrote:
> > On Mon, 2009-11-09 at 21:31 +0900, Kenji Kaneshige wrote:
> > > Hi,
> > >
> > > I frequently encounter the kernel oops attached below in resched_task()
> > > with 2.6.31.5. This kernel oops happens also with 2.6.32-rc5. I don't
> > > know about other kernel.
> > >
> > > Here is my analysis:
> > >
> > > The immediate cause of this kernel oops is that NULL was passed to
> > > resched_task() from resched_cpu(). From my investigation, this was
> > > caused as follows:
> > >
> > > - trigger_load_balance() caluculated cpu number of idle load balancer
> > >   using find_new_ilb(), and find_new_ilb() returned *offline* CPU
> > >   number (16 in my case). Note that I didn't do any CPU hotplug
> > >   operation. On my system, present, online and offline under
> > >   /sys/devices/system/cpu/ are
> > >
> > >     [kanesige@localhost ~]$ cat /sys/devices/system/cpu/present
> > >     0-15
> > >     [kanesige@localhost ~]$ cat /sys/devices/system/cpu/online
> > >     0-15
> > >     [kanesige@localhost ~]$ cat /sys/devices/system/cpu/offline
> > >     16-255
> > >
> > >   And nr_cpu_ids is 256.
> > >
> > > - resched_cpu() calculated current task by cpu_curr() with offline CPU
> > >   number.
> > >
> > > So this kernel oops seems to be caused by invalid CPU number returned
> > > from find_new_ilb(). I don't know the find_new_ilb() implementation,
> > > but I suspect the initialization of cpumasks used by find_new_ilb().
> > > The patch attached below seems to fix the problem (With this patch,
> > > the kernel oops doesn't happen). But I don't know if this is the
> > > correct fix.
> >
> > Please send patches against -tip.
> >
> > You might find that Rusty has already fixed a similar issue there in
> > commit: 49557e620339cb134127b5bfbcfecc06b77d0232.
> >
> > Now, Rusty's patch does not clear the ilb mask, so maybe it doesn't
> > fully cover your issue, please test.
>
> Thank you for quick response.
>
> I didn't notice Rusty's fix.
> I'll look at and test it tomorrow.

I tested Rusty's patch and confirmed it fixes the problem.

Thanks,
Kenji Kaneshige


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/